Apparatus for adjusting a camshaft, and method for operating an apparatus for adjusting a camshaft

ABSTRACT

In an apparatus for adjusting a phase position of a camshaft in relation to a crankshaft which drives the camshaft, including an electric actuator for operating an adjustment mechanism, which can move the camshaft to a basic or emergency-operating position in the event of a shut-down as a result of an operational fault, the emergency-operating position can be reliably reached with the aid of the electric actuator which is supplied with energy by an energy supply that is separate from an operational energy supply and which is capable of moving the adjustment mechanism to the emergency-operating position. Also, a method for operating an apparatus for adjusting a phase position of a camshaft is provided.

This is a Continuation-In-Part Application of pending International patent application PCT/EP2005/008449 filed Aug. 4, 2005 and claiming the priority of German patent application 10 2004 038 171.2 filed Aug. 6, 2004.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for adjusting the phase position of a camshaft relative to a crankshaft driving the camshaft, and to a method of operating an apparatus for adjusting a camshaft.

It is known to change the phase position of a camshaft of an internal when the engine is turned off, combustion engine using adjusting devices. Normally, the camshaft is moved to a particular basic position and fixed in this position. In the case of electric adjusting devices, a separately energized electric adjuster or an electric adjuster with permanent-magnet excitation, for example, is used for this purpose, whereas a hydraulic rotary piston adjuster which has a locking unit is used in the case of hydraulic adjusting devices. The locking unit fixes the hydraulic adjuster in its basic position until a sufficiently high oil pressure for adjusting the camshaft has built up after star-up of the internal combustion engine.

When the internal combustion engine stalls, it is not possible to adjust the hydraulic adjuster in a controlled manner, with the result that the camshaft may be in an undefined position outside the basic position. When the vehicle is next started, the camshaft must therefore be moved to a suitable basic position, for example by a compensation spring. In the case of electric adjusters, no additional measure is required when restarting following stalling of the internal combustion engine since the adjuster can move the camshaft to the respective basic position even when the internal combustion engine is shut down or during startup operations. However, in the case of electric adjusting devices, the adjuster and/or its controller may fail and thus not reach the basic or emergency-operation position which is required for at least restricted operation so that, as a result, the engine cannot be started. By way of example, adjusting devices with restoring springs which allow an emergency-operation position to be reached, but which involve increased power consumption and unattractive system dynamics and also require a relatively large installation space, are known.

DE 102 57 706 A1 discloses an adjusting device for a camshaft, wherein the camshaft is adjusted in the direction of an early or late basic or emergency-operation position by simply braking the adjusting shaft if the adjuster or its power supply fails while the adjustment mechanism is rotating.

It is the principle object of the present invention to provide an adjusting device for a camshaft, in which adjusting device a basic or emergency-operating position can be reliably reached in the event of an operational fault. It also is an object to provide a method for operating such an device.

SUMMARY OF THE INVENTION

In an apparatus for adjusting a phase position of a camshaft in relation to a crankshaft which drives the camshaft, including an electric actuator for operating an adjustment mechanism, which can move the camshaft to a basic or emergency-operating position in the event of a shut-down as a result of an operational fault, the emergency-operating position can be reliably reached with the aid of the electric actuator which is supplied with energy by an energy supply that is separate from an operational energy supply and which is capable of moving the adjustment mechanism to the emergency-operating position. Also, a method for operating an apparatus for adjusting a phase position of a camshaft is provided.

An inventive apparatus for adjusting a phase position of a camshaft in relation to a crankshaft which drives the camshaft has an actuator which can be supplied with energy by an energy supply which is separate from its operating supply in order to move the adjustment mechanism to the basic or emergency-operating position. As a result, the actuator can be supplied with operating power by a second supply system which is independent of an operating supply of the apparatus for a brief period of time in the event of an operational fault, which is highly cost-effective and operationally reliable. Furthermore, the basic or emergency-operation position can also be advantageously assumed in the event of normal shut-down of the internal combustion engine.

If the separate energy supply comprises an energy store, by means of which the actuator can be supplied with energy, the actuator can move the adjustment mechanism to a desired position in a targeted manner in the event of an operational fault. The energy store is preferably an electrical storage means for an electrically operable actuator. However, other energy stores for other types of actuator and kinds of adjusting apparatuses, for example a hydraulic storage means for a hydraulic adjusting apparatus, are also conceivable.

The separate energy supply can expediently be activated by an engine controller which actuates the internal combustion engine. If an operational fault is identified, the engine controller can quickly operate the energy supply in order to provide power for activating the actuator.

In one favorable embodiment, the energy store comprises a storage battery. As an alternative, or in addition, the energy store may comprise a particularly preferred capacitor. Said capacitor is particularly highly suited to rapid discharging. If necessary, the actuator can be supplied with current from the capacitor of a brief period, for a few hundred milliseconds, for example typically 200 ms, in order to move the adjustment mechanism to a desired position. The basic or emergency-operation position can be reached at the latest after approximately 300 ms. The basic or emergency-operation position preferably corresponds to a locked position, with the adjustment mechanism crossing a locking unit when the actuator drives the adjustment mechanism. The energy store is advantageously of small design since only a low power content is required for such a brief operation. This is advantageous, for example, for feeding the content of the storage means to a hysteresis brake for a brief period of time, and in this way moving the camshaft to its basic or emergency operating position.

In a favorable refinement, the separate energy supply comprises a separate connection to an on-board vehicle electrical system, which connection is separate from the normal operating energy supply for the actuator. The separate energy supply is expediently accessible with a certain safety level in the engine controller.

It is particularly favorable when the adjusting device is designed such that it automatically moves to a defined end stop position when it or the actuator is de-energized.

In one particularly preferred refinement, the actuator is in the form of a hysteresis brake. The actuator preferably has a separate auxiliary coil which can be actuated in the event of an operational fault in the field coil of the actuator. In this case, in spite of a defective field coil, a magnetic field can still be built up in the hysteresis brake in order to brake the adjustment mechanism. The auxiliary coil expediently has a high impedance that is it has as many turns as possible, these turns being wound around a stator of the actuator. The auxiliary coil is expediently supplied with power by the energy store, which is independent of the operating energy supply. Although the provision of as many turns as possible increases the electrical time constant of the auxiliary coil, which also results in a reduction in power consumption, and this is advantageous in terms of the size of the energy store.

According to the inventive method for operating an apparatus for adjusting a phase position of a camshaft, an actuator which operates an adjustment mechanism is supplied with energy by an energy supply which is separate from the operating supply in order to move the adjustment mechanism to a basic or emergency-operation position.

If the adjustment mechanism automatically moves to a defined, first end stop position in the de-energized state, a locking device, which determines the basic or emergency-operating position, can be reliably reached or crossed as a result of a movement of the adjustment mechanism toward a second end stop position which is provided by the actuator supplied by the separate energy supply. If the adjustment mechanism was already on the other side of this locking device in terms of the direction of rotation, the adjustment mechanism automatically returns to the defined first end stop position after the energy store has been emptied and, with a brief delay, then reaches the locking device, is locked there and is thus in its basic and emergency-operation position.

The adjustment mechanism is expediently retained in the locking position; in particular, the adjustment mechanism is latched in place in the locked position.

An exemplary embodiment of the invention will be described below in greater detail with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a preferred apparatus for adjusting a camshaft, having an energy store; and

FIG. 2 shows schematically a preferred apparatus for adjusting a camshaft, having a separate connection to an on-board vehicle electrical system.

DESCRIPTION OF PARTICULAR EMBODIMENTS

As can be seen from FIG. 1, a particularly preferred apparatus 10 for adjusting a phase position of a camshaft 12 in relation to a crankshaft (not illustrated) which drives the camshaft 12 comprises an actuator 15, which is in the form of a hysteresis brake, for operating an adjustment mechanism 11. The adjustment mechanism 11 can be driven by a drive 13 which is in the form of a drive wheel and is connected to the crankshaft, for example, via a drive chain. The drive 13 surrounds the adjustment mechanism 11 in a concentric manner. The actuator 15, which is in the form of an electrically operable actuator, in particular in the form of a hysteresis brake, is operatively connected to an actuating input 14 to the adjustment mechanism 11. An axis of rotation of the actuator 15 is indicated as a dash-dotted line. The adjustment mechanism 11 may, for example, be a planetary gear mechanism, a wobble gear mechanism or an eccentric gear mechanism. The actuator 15, which is in the form of a hysteresis brake, comprises a field coil 26 which provides a holding torque or a drive torque for holding or adjusting the adjustment mechanism 11 during energization.

During normal operation, the field coil 26 is supplied with energy by a customary on-board vehicle electrical system 16, and this is schematically indicated by supply lines 17 and 18. An engine controller 23 is also provided, which engine controller is connected to the on-board vehicle electrical system 16. This is indicated by a double-headed arrow 24 between the on-board vehicle electrical system 16 and the engine controller 23.

In order to move the actuator 15 to its basic or emergency-operating position, a separate energy supply is provided consistent of a separate energy store 19 which can be actuated by the engine controller 23. The connection between the engine controller 23 and the energy store 19 is indicated by a double-headed arrow 25. In order to quickly operate the actuator 15 in the event of an operational fault, the energy store 19 comprises a storage battery and/or preferably a capacitor. Supply lines 20, 21 are provided between the energy store 19 and the actuator 15 in order to supply the actuator 15 with electrical energy as required.

The adjustment mechanism 11 is designed such that it automatically moves to a defined first end stop when the hysteresis brake is in the de-energized state. In the event of a fault, the actuator 15, which operates the adjustment mechanism 11, is supplied with current from the energy store 19, which is preferably a capacitor, for a brief period of approximately 200 ms, so as to move in the direction toward another, second end stop. In the process, a locking device is passed, which locking device can latch the adjustment mechanism 11 in place and thus fix the adjustment mechanism 11 in its basic or emergency-operating position. If the adjustment mechanism 11 was already on the other side of the locking device, it automatically moves, after the capacitor is drained and depending on its design, in the direction toward the defined first end stop and reaches the locking position from the other side. The locking position is therefore reliably reached, independently of the actual position of the adjustment mechanism. The adjustment mechanism 11 reaches its basic or emergency-operating position after a brief time, for example at the latest after 300 ms, following a power loss.

FIG. 2 shows an alternative embodiment. Identical elements are designated by the same reference symbols as in FIG. 1. The design corresponds to that of FIG. 1, to which reference is made for explanatory purposes. Instead of an energy store 19 (FIG. 1), the separate energy supply provided is now a connection 22 to an on-board vehicle electrical system 16′, which connection is separate from the normal operating power supply. In this case, an actuator 15, which is in the form of a hysteresis brake, has a separate auxiliary coil 27 which can be actuated by an engine controller 23 in the event of an operational fault in a field coil 26 of the actuator 15, and this is indicated by arrows 24 between the engine controller 23 and the on-board vehicle electrical system 16.

The auxiliary coil 27 has a high impedance in order to still build up a magnetic field in the hysteresis brake with a relatively low power requirement in the event of a defect in a field coil 26 of the hysteresis brake. The auxiliary coil 27 is wound around a stator of the hysteresis brake. 

1. An apparatus for adjusting a phase position of a camshaft (12) in relation to a crankshaft which drives the camshaft (12), said apparatus including an adjustment mechanism for adjusting the phase position of the camshaft relative to the camshaft, an actuator (15) for operating the adjustment mechanism (11), the camshaft (12) being movable to an emergency-operating position in the event of a shut-down as a result of an operational fault, and an energy supply (19, 22) separate from an operating energy supply provided for the actuator (15) for supplying energy thereto for moving the adjustment mechanism (11) to the emergency-operating position.
 2. The apparatus as claimed in claim 1, wherein the separate energy supply (19, 22) comprises an energy store (19), by which the actuator (15) can be supplied with energy for a brief period of time.
 3. The apparatus as claimed in claim 1, wherein the separate energy supply (19, 22) is activatable by an engine controller (23).
 4. The apparatus as claimed in claim 1, wherein the energy supply (19) comprises a storage battery.
 5. The apparatus as claimed in claim 1, wherein the energy supply (19) comprises a capacitor.
 6. The apparatus as claimed in claim 1, wherein the separate energy supply (19, 22) comprises a connection (22) to an on-board vehicle electrical system (16), which connection is independent of the operating supply.
 7. The apparatus as claimed in claim 1, wherein the adjustment mechanism (11) is designed such that it automatically moves to a first end stop position when the actuator (15) is in the de-energized state.
 8. The apparatus as claimed in claim 1, wherein the actuator (15) is in the form of an electric brake.
 9. The apparatus as claimed in claim 1, wherein the actuator (15) is in the form of a hysteresis brake.
 10. The apparatus as claimed in claim 9, wherein the hysteresis brake has a separate auxiliary coil (27) which is actuatable in the event of an operational fault in a field coil (26) of the hysteresis brake.
 11. A method for operating an apparatus for adjusting a phase position of a camshaft (12) in relation to a crankshaft which drives the camshaft (12), the apparatus including an electric actuator (15) for operating an adjustment mechanism (11), with the camshaft (12) being movable to an emergency-operating position in the event of a shut-down as a result of an operational fault, said method comprising the steps of supplying the actuator (15) with energy from an energy supply (19, 22) which is separate from its normal operating energy supply for moving the adjustment mechanism (11) to the emergency-operating position.
 12. The method as claimed in claim 11, wherein, in the de-energized state, the adjustment mechanism (11) automatically moves to a first end stop position.
 13. The method as claimed in claim 11, wherein the adjustment mechanism (11) is moved in the direction toward a second end stop position by the actuator (15) which can be supplied with power by the separate energy supply (19, 22), for reaching a locking position in which the adjustment mechanism (11) is then locked.
 14. The method as claimed in claim 13, wherein the adjustment mechanism (11) is firmly engaged in the locked position. 